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Command Cheat Sheet

All the tips and tricks that I have found useful are here!

Kernel version, hostname, date and architecture​

uname -a

Output example:

Linux ubuntu 5.15.0-52-generic #58-Ubuntu SMP Tue Jun 28 14:27:29 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

Get the distribution name and version​

lsb_release -a

Output example:

No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 22.04.4 LTS
Release:	22.04
Codename:	jammy

Get installed kernel version​

dpkg --list | grep linux-image

Output example:

ii  linux-image-5.15.0-52-generic             5.15.0-52.58~22.04.1                    amd64        Signed kernel image generic

Install a specific kernel version​

sudo apt install \
linux-headers-5.15.0-52-generic \
linux-image-5.15.0-52-generic \
linux-modules-5.15.0-52-generic \
linux-modules-extra-5.15.0-52-generic

Or remove a specific kernel version ...

sudo apt purge \
linux-headers-5.15.0-52-generic \
linux-image-5.15.0-52-generic \
linux-modules-5.15.0-52-generic \
linux-modules-extra-5.15.0-52-generic

Timezone​

Get the current timezone

timedatectl status

Output example:

Local time: Fri 2022-07-01 14:27:29 UTC
Universal time: Fri 2022-07-01 14:27:29 UTC
RTC time: Fri 2022-07-01 14:27:29
Time zone: UTC (UTC, +0000)
System clock synchronized: yes
NTP service: active
RTC in local TZ: no

Change the timezone

sudo timedatectl set-timezone Europe/Paris

Then, reboot the system.

caution

When you are running Cron jobs, you need to make sure that the timezone is set correctly. Otherwise, the jobs will run at the wrong time.

Get the system uptime​

uptime

Kill a process​

kill -9 pid_number
tip

To find the pid_number of a process, use the ps command or ps aux to see all process, or top command.

Coupled with grep to filter the process you want to kill, example:

ps aux | grep process_name

Avoid typing password as sudo​

sudo visudo

And add it to the end of the file:

username ALL=(ALL) NOPASSWD: ALL

Get the IP address of the machine​

ip addr show

List all the rules in the iptables​

sudo iptables -L -n -v

Allow traffic by CIDR using iptables​

sudo iptables --insert INPUT --source 10.0.0.0/8 --jump ACCEPT && \
sudo iptables --insert INPUT --destination 10.0.0.0/8 --jump ACCEPT && \
sudo iptables --insert FORWARD --source 10.0.0.0/8 --jump ACCEPT && \
sudo iptables --insert FORWARD --destination 10.0.0.0/8 --jump ACCEPT && \
sudo iptables --insert OUTPUT --source 10.0.0.0/8 --jump ACCEPT && \
sudo iptables --insert OUTPUT --destination 10.0.0.0/8 --jump ACCEPT && \
sudo netfilter-persistent save && \
sudo netfilter-persistent reload
info

For instance, this CIDR 10.0.0.0/8 contains all the IP addresses from 10.0.0.0 to 10.255.255.255

This website can help you to find the CIDR of a specific IP address.

Open a specific port​

sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT
sudo iptables -I INPUT 6 -m state --state NEW -p tcp --dport 80 -j ACCEPT

Reset the iptables and flush all the rules​

sudo iptables -F
sudo iptables -X

Disk free space​

df -kh

-k is for kilobytes, -h is for human readable.

Output example:

Filesystem      Size  Used Avail Use% Mounted on
tmpfs           2.4G  1.4M  2.4G   1% /run
/dev/sda1       194G  2.5G  192G   2% /
tmpfs            12G     0   12G   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
/dev/sda15       98M  6.3M   92M   7% /boot/efi
tmpfs           2.4G  4.0K  2.4G   1% /run/user/1001

Disk usage​

sudo du -hs /

-h is for human readable, -s is for summary.

Output example:

2.5G    /

Ping​

It is possible to reduce the default delay (1 second) of ping command (recently minimum time was changed to 200ms = 0.2).

ping -i 0.2 server.com

Root can issue shorter time.

sudo ping -i 0.01 server.com

Files and directories​

Base64​

Encode a file to base64

base64 file.txt

Decode a base64 file

base64 --decode file.txt

Encode from stdin to base64

echo "Hello World" | base64

Decode from stdin to base64

echo "SGVsbG8gV29ybGQ=" | base64 --decode

Find a file​

Find is a command-line utility for searching files and directories in a Unix-like computer operating systems.

find [where to start searching from] [expression determines what to find] [-options] [what to find]`

Find a file

find /directory -name "file.txt"

Find a file with a pattern

find /directory -name "*file*.txt"

Git​

Graphical logs​

git log --oneline --graph --decorate --all

A full example:

git log --all --graph --abbrev-commit --decorate --format=format:'%C(bold blue)%h%C(reset) - %C(bold cyan)%aD%C(reset) %C(bold green)(%ar)%C(reset)%C(bold yellow)%d%C(reset)%n''%s%C(reset) %C(dim)- %an%C(reset)'

Rebase​

For instance, a git rebase interactive from your current branch, to the 3 previous commits:

git rebase -i HEAD~3
tip

The shortcut of HEAD is @.

git rebase -i @~3
tip

HEAD is the current branch. HEAD~1 is the previous commit. HEAD~2 is the commit before the previous one. And so on.

An other example, a git rebase interactive from the current branch, to the commit 123456789:

git rebase -i 123456789

And finally, a git rebase interactive from the current branch, to the previous commit 123456789:

git rebase -i 123456789^

Or with the tilde shortcut:

git rebase -i 123456789~